In powdered materials technology devices are known which are commonly called fluid bed granulator devices, generally used for the treatment of the materials and basically comprising containers with sealed walls, delimiting a chamber for treatment of the materials, permanent filters, with solid walls, projecting into the treatment chamber, means for conveying an operating fluid current through the chamber, and means designed to perform operations which remove powder from and wash the permanent filters.
The operations for removing powder from and washing the filters, designed to restore the original functionality of filters clogged or whose efficiency was reduced by use, or to prepare the device to treat a different product to that treated in a previous processing cycle, have quite a critical role in many powder technologies used, for example, for some chemical or pharmaceutical products.
Such operations must be performed in a suitable way to prevent the operating fluids entering the device from contaminating the product and/or the operating fluids fed out of the device from contaminating the environment, and/or maintenance operations on the filters and on the other operating parts of the device from constituting a health risk for the personnel who carry them out, and for the surrounding environment.
A granulator device of the type described above is known, for example, in patent EP 781.585 B1, in which the permanent filters have rigid filtering walls formed by two or more overlapping layers of metal mesh which are made integral with one another by a sintering process.
Therefore, powder is removed from the filters and they are washed respectively by blowing counterflowing pressurised air through the filtering wall, the air emitted from stationary nozzles covering the entire extent of the filtering surface of each of the filters, and by washing down the outer surface of the filters by directing a flow of water diffused from special nozzles, also stably supported by the outer walls of the container which circumscribes the product treatment chamber.
A device structured in this way allows satisfactory filter cleaning for most applications, in particular during the treatment of powdered products for pharmaceutical use, but is very complex from a construction viewpoint, very expensive and it is particularly difficult to check its effectiveness.
For these reasons, granulator devices are currently known and used which are made as separable modules with independent drive units, so that maintenance personnel find it easier to manually remove powder from and wash the filters when they are permanent, or granulator devices with filter means consisting of bags of special filtering fabrics applied on metal wire frame supporting structures, such as that described and illustrated in United States patent U.S. Pat. No. 5,723,160, so that maintenance operations simply consist of substituting the filter bags.
However, such fabric filters are particularly expensive and their simple substitution involves opening the above-mentioned treatment chamber, and so inevitably contamination of the chamber by external agents.